1. Field of the Invention
This invention relates to a base plate with electrodes, which base plate is provided with a plurality of electrodes having been formed in a predetermined pattern, and a process for producing the base plate with electrodes. This invention also relates to an electro-optical device and an electroluminescent device, each of which comprises the base plate with electrodes.
2. Description of the Related Art
Electroluminescent devices (EL devices) are self-emitting devices having a structure in which at least a lower electrode, a light emitting layer capable of emitting light with voltage application or electric current application, and an upper electrode are overlaid on a base plate.
FIG. 8 is a fragmentary sectional view taken in a thickness direction of a conventional EL device, the view acting as an aid in explaining problems encountered with the conventional EL device. As illustrated in FIG. 8, a lower electrode 120 is formed in a predetermined pattern on a base plate 110. Also, a light emitting layer 140 and an upper electrode 150 are overlaid so as to extend through a region on the lower electrode 120 and through an adjacent electrode gap. In such cases, there is a tendency for the layer thickness of the region of the light emitting layer 140, which region is located along the side face of the lower electrode 120, to become thinner than the layer thicknesses of the other regions of the light emitting layer 140.
More of the electric current is apt to flow through the thin region of the light emitting layer 140 than through the other regions of the light emitting layer 140. Therefore, the electric current flows preferentially among the upper electrode 150, and the thin region of the light emitting layer 140, which region is located along the side face of the lower electrode 120 and is not required to emit the light, and the lower electrode 120. The thus flowing electric current is an unnecessary leak current.
In cases where the leak current flows through the region of the light emitting layer 140, which region is located along the side face of the lower electrode 120, there is the risk that the quantity of the electric current flowing through the region of the light emitting layer 140, which region is located on the top surface of the lower electrode 120 and is required to emit the light, will become small, and that a desired light emission intensity will not be capable of being obtained. Also, there is the risk that the light emission quantities with respect to pixels will become nonuniform, and that nonuniformity in light emission pattern will occur.
Further, in cases where the electric current flows preferentially through the region of the light emitting layer 140, which region is located along the side face of the lower electrode 120 and is formed so as to have the small layer thickness, the region of the light emitting layer 140 deteriorates comparatively quickly, and the layer thickness of the region of the light emitting layer 140 becomes thin quickly. Therefore, in cases where the period of time of use becomes long, the problems described above are aggravated. If the layer thickness of the region of the light emitting layer 140, which region is located along the side face of the lower electrode 120, becomes markedly small, there will be the risk that short-circuiting will occur between the lower electrode 120 and the upper electrode 150.
An EL device provided with a black matrix (EM) for blocking off electrode gaps of a plurality of lower electrodes is disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-359083. The disclosed EL device is produced with a process comprising the steps of: (a) forming a film of an electrode material on a base plate, an electrical conductor layer being thereby formed on the base plate, (b) performing coating, exposure, and development of a resist, a resist pattern in accordance with a pattern of lower electrodes being thereby formed, (c) etching the electrical conductor layer with the resist pattern acting as a mask, the pattern of the plurality of the lower electrodes being thereby formed, (d) removing the resist pattern, and (e) performing coating, exposure, and development of a different resist, a BM for blocking off electrode gaps of the plurality of the lower electrodes being thereby formed.
With the EL device disclosed fin, for example, Japanese Unexamined Patent Publication No. 2002-359083, the side face of each of the lower electrodes is covered with the BM having the electrical insulation characteristics. Therefore, the occurrence of the leak current flowing through the side face of each of the lower electrodes is capable of being suppressed. However, with the EL device disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-359083, besides the exposure of the resist for the formation of the patterning mask for the lower electrodes, it is necessary for the exposure of the resist for the formation of the BM to be performed. Accordingly, the number of the processing steps is not capable of being kept small, and the production efficiency is not capable of being kept high. Also, there is the risk that a fine gap will occur between the side face of each of the lower electrodes and the BM due to a shift of alignment of the photomask occurring at the time of the exposure of the resist for the formation of the BM to light. In such cases, the side face of each of the lower electrodes will not be capable of being accurately covered with the BM, and the occurrence of the leak current flowing through the side face of each of the lower electrodes will not be capable of being suppressed.
As illustrated in, for example, FIG. 3 of Japanese Unexamined Patent Publication No. 2002-359083, with the shift of the alignment of the photomask being taken into the consideration, part of each of the lower electrodes and part of the BM may be caused to overlap each other. In such cases, the side face of each of the lower electrodes is capable of being reliably imparted with the electrical insulation characteristics. However, in such cases, the problems occur in that an open face rate of the lower electrodes is not capable of being kept high. In cases where pitches of the lower electrodes are set at large values, though the open face rate of the lower electrodes becomes low, a large open face area of the lower electrodes is capable of being obtained. However, in such cases, the problems occur in that the resolution becomes low, and displaying quality is not capable of being kept good.
The adverse effects of the occurrence of the leak current, which flows through the side face of each of the electrodes, upon the displaying quality, the reliability, and the like, are comparatively large in the cases of the EL device. The problems with regard to the occurrence of the leak current, which flows through the side face of each of the electrodes, may occur also with liquid crystal devices, in which electrodes are formed on an inside surface of at least either one of a pair of base plates located so as to stand facing each other with a liquid crystal layer intervening there between.